Grafting of nano-TiO2 onto flax fibers and the enhancement of the mechanical properties of the flax fiber and flax fiber/epoxy composite

In this article, a flax fiber yarn was grafted with nanometer sized TiO₂, and the effects on the tensile and bonding properties of the single fibers and unidirectional fiber reinforced epoxy plates were studied. The flax fiber yarn was grafted with nanometer sized TiO₂ through immersion in nano-TiO₂/KH560 suspensions under sonification. The measured grafting content of the nano-TiO₂ ranged from 0.89 wt.% to 7.14 wt.%, dependent on the suspension concentration. With the optimized nano-TiO₂ grafting content (∼2.34 wt.%), the tensile strength of the flax fibers and the interfacial shear strength to an epoxy resin were enhanced by 23.1% and 40.5%, respectively. The formation of Si–O–Ti and C–O–Si bonds and the presence of the nano-TiO₂ particles on the fiber surfaces contributed to the property enhancements. Unidirectional flax fiber reinforced epoxy composite (V_f = 35.4%) plates prepared manually showed significantly enhanced flexural properties with the grafting of nano-TiO₂.     

Enhanced mechanical properties of multiscale carbon fiber/epoxy composites by fiber surface treatment with graphene oxide/polyhedral oligomeric silsesquioxane

Graphene oxide (GO) and polyhedral oligomeric silsesquioxane (POSS) grafted carbon fiber (CF) was demonstrated to reinforce the mechanical properties of fiber composites. Such a fiber composite was prepared by grafting POSS onto the CF surface using GO as the linkage. The presence of GO linkage and POSS could significantly enhance both the area and wettability of fiber surface, leading to an increase in the interfacial strength between fibers and resin. Compared with the desized CF composites, the grafted CF composites fabricated by compression molding method exhibited 53.05% enhancement in the interlaminar shear strength. The changed surface morphology, surface composition and surface energy were supposed to be related with the interfacial performance of unidirectional composites, as revealed by scanning electron microscopy, atomic force microscope, dynamic contact angle test and X-ray photoelectron microscopy charaterizations.     

Effect of γ-ray irradiation grafting on the carbon fibers and interfacial adhesion of epoxy composites

A special technique using γ-ray irradiation-induced graft-polymerization was applied to carbon fibers. Epoxy resin and chloroepoxy propane reacted with carbon fibers by a co-irradiation grafting method and acrylic acid was graft-polymerized onto the fiber surface via a pre-irradiation grafting method. The roughness, amount of containing-oxygen functional groups and surface energy were all found to increase significantly after irradiation grafting. Gamma-ray irradiation grafting improved marginally the tensile strength of carbon fibers, which was evaluated by statistical analysis using the Weibull distribution. The interlaminar shear strength of treated carbon fiber/epoxy was enhanced by at least 17.5%, compared with that of untreated carbon fiber/epoxy. The mechanisms of irradiation grafting are proposed by radical reactions. The γ-ray co-irradiation grafting and pre-irradiation grafting are both an effective method for modifying the physicochemical properties of carbon fibers and improving the interfacial adhesion of composites.     

Effects of treatment with low molecular weight phenol formaldehyde resin on the surface characteristics of oil palm (Elaeis quineensis) stem veneer

Even though oil palm (Elaeis quineensis) stem (OPS) is highly potential as an alternative raw material in wood industry, it possesses some inferior characteristics. One of the critical weaknesses is a high degree of veneer surface roughness that resulted in high resin consumption during plywood manufacture. The objective of this study was to investigate effects of treatment with low molecular weight phenol formaldehyde (LMWPF) resin on the wettability and surface roughness of OPS veneer. OPS veneers were segregated into two categories namely outer and inner layer veneer, prior to soaking in LMWPF resin solution to obtain weight percent gain of 16–20%. The wettability of OPS veneers was assessed with contact angle measurement according to the sessile drop method. The veneer surface roughness was evaluated by determining the average roughness (R_a), mean peak-to-valley height (R_z), and maximum roughness (R_max) using a stylus profilometer in accordance with DIN standard 4768. The results show that the effect of LMWPF resin treatment on the surface roughness of the veneers is statistically significant. The technique used in the study was able to enhance the surface properties as well as improved the physical and mechanical properties of OPS plywood.     

Improvement of epoxy resin properties by incorporation of TiO2 nanoparticles surface modified with gallic acid esters

Epoxy resin/titanium dioxide (epoxy/TiO₂) nanocomposites were obtained by incorporation of TiO₂ nanoparticles surface modified with gallic acid esters in epoxy resin. TiO₂ nanoparticles were obtained by acid catalyzed hydrolysis of titanium isopropoxide and their structural characterization was performed by X-ray diffraction and transmission electron microscopy. Three gallic acid esters, having different hydrophobic part, were used for surface modification of the synthesized TiO₂ nanoparticles: propyl, hexyl and lauryl gallate. The gallate chemisorption onto surface of TiO₂ nanoparticles was confirmed by Fourier transform infrared and ultraviolet–visible spectroscopy, while the amount of surface-bonded gallates was determined using thermogravimetric analysis. The influence of the surface modified TiO₂ nanoparticles, as well as the length of hydrophobic part of the gallate used for surface modification of TiO₂ nanoparticles, on glass transition temperature, barrier, dielectric and anticorrosive properties of epoxy resin was investigated by differential scanning calorimetry, water vapor transmission test, dielectric spectroscopy, electrochemical impedance spectroscopy and polarization measurements. Incorporation of surface modified TiO₂ nanoparticles in epoxy resin caused increase of glass transition temperature and decrease of the water vapor permeability of epoxy resin. The water vapor transmission rate of epoxy/TiO₂ nanocomposites was reduced with increasing hydrophobic part chain length of gallate ligand. Dielectric constant of examined nanocomposites was influenced by gallate used for the modification of TiO₂ nanoparticles. The nanocomposites have better anticorrosive properties than pure epoxy resin, because the surface modified TiO₂ nanoparticles react as oxygen scavengers, which inhibit steel corrosion by cathodic mechanism.     

Interfacial properties and impact toughness of methylphenylsilicone resin composites by chemically grafting POSS and tetraethylenepentamine onto carbon fibers

Octaglycidyl polyhedral oligomeric silsesquioxane (gly-POSS) was successfully grafted on carbon fibers (CFs) surface to enhance interfacial properties and impact toughness of CFs reinforced methylphenylsilicone resin (MPSR) composites. After gly-POSS modification, POSS grafted CF (CF-POSS) with many epoxy functional groups was modified with tetraethylenepentamine (TEPA) to further enhance the interfacial strength. Atomic force microscopy (AFM) images showed that POSS and TEPA were grafted onto CFs surface uniformly and the surface roughness enhanced obviously. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed the chemical bonding nature between CFs and POSS, as well as between POSS and TEPA. POSS and TEPA modification could increase the fiber polarity, wettability and surface energy significantly. The interlaminar shear strength (ILSS) and impact toughness of composites showed a dramatic improvement, especially for grafting with POSS and further with TEPA (CF-POSS-TEPA). Additionally, the reinforcing and toughening mechanisms were also analyzed. Meanwhile, single fiber tensile strength (TS) had no decrease after modification.     

Studies on mechanical properties of epoxy composites filled with the grafted particles PGMA/Al2O3

In the present work, the epoxy resin composites filled with the particulates of PGMA/Al₂O₃ which were prepared by grafting poly-glycidyl methacrylate (PGMA) onto the Al₂O₃, were obtained by incorporating and curing the resin containing the particulates. The mechanical properties of the resulting resin composites epoxy/PGMA/Al₂O₃ were evaluated and compared with epoxy/Al₂O₃. The morphologies of the fracture surfaces of the filled epoxy resin composites were analyzed by means of scanning electron microscopy (SEM). The results indicate that after grafting polymers onto Al₂O₃ particles, the interfacial combination of epoxy resin with PGMA/Al₂O₃ can be significantly increased due to the higher bonding strength and bonding modulus between them, therefore, the properties of the composites are improved largely. And the higher grafting degree of PGMA, the greater the impact strength and yield strength of the resin composites are, which primarily depends on the structure-properties relationship of the composites. In addition, the additive amount of PGMA/Al₂O₃ particles and the curing agents are also important factors that influence the properties of composites.     

纳米SiO2表面接枝聚合改性及其聚丙烯基复合材料的力学性能

分别用苯乙烯和丙烯酸乙酯对纳米SiO₂进行辐照接枝聚合改性,通过两步熔融共混工艺与聚丙烯(PP)共混制备了SiO₂/PP复合材料。研究了SiO₂添加量和表面接枝不同聚合物的SiO₂对复合材料力学性能的影响。结果表明,接枝改性的SiO₂对PP有较好的增强增韧效果;拉伸断面观察显示复合材料韧性的提高主要由基体剪切屈服所致。对断面上个别较大团聚体分析发现,经辐照接枝聚合改性的纳米粒子团聚体的结构变得更加紧凑、结实,且随粒子表面聚合物的性质不同,团聚体与基体树脂的界面粘结也随之不同,导致其拉伸破坏形状有所差异,但与基体树脂的界面粘结都得到较好的改善。     

Enhancing the grafting of poly(2-hydroxyethyl methacrylate) on silica nanoparticles (SiO2-g-PHEMA) by the sequential UV-induced graft polymerization with a multiple-UV irradiation

Grafting of poly(2-hydroxyethyl methacrylate) on silica nanoparticles was accomplished via the sequential UV-induced graft polymerization. Under UV-irradiation, the silica was functionalized with the surface initiator, benzophenone (BP) and subsequently graft-polymerized with 2-hydroxyethyl methacrylate (HEMA). The grafting on the silica particles was confirmed by DSC analysis which revealed a shift of the glass transition temperature (T_g) of grafted PHEMA to higher temperature than T_g of ungrafted PHEMA. A significant improvement in the grafting efficiency and the grafting percentage was achieved when a sequential grafting approach was taken, employing multiple UV exposures. Using this approach, the efficient chain extension from the grafted-PHEMA was possible without producing significant amounts of ungrafted PHEMA when low HEMA concentrations were used during each UV-exposure.     

Study of strontium- and magnesium-doped lanthanum gallate solid electrolyte surface by X-ray photoelectron spectroscopy

The chemical states of the surface of the oxygen ion conducting solid electrolyte La_0.9Sr_0.1Ga_0.85Mg_0.15O_3−δ (LSGM 1015) as prepared by solid-state synthesis was analyzed by X-ray photoelectron spectroscopy. It was found that adventitious carbon did not interact with any of the constituent elements of LSGM 1015. Ga and La were found to exist in trivalent states. But, due to ionic bombardment presence of Mg could not be detected in the electrolyte surface.     

Kevlar－49芳纶纤维表面接枝改性

采用空气等离子体处理Ｋｅｖｌａｒ－４９并在活化处理后的纤维表面接枝聚丙烯酸（ＰＡＡ）、聚丙烯酸乙酯（ＰＥＡ）及丙烯酸和丙烯酸乙酯的共聚物（ＰＡＡ／ＥＡ）。单丝拔出实验研究表明，空气等离子体改性的Ｋｅｖｌａｒ－４９／环氧树脂体系的界面结合强度和界面破坏能均有明显提高，其中接枝了Ｐ（ＡＡ／ＥＡ）的Ｋｅｖｌａｒ－４９／环氧树脂体系的界面破坏能（５５Ｊ／ｍ２）比未改性体系的界面破坏能（２７．８Ｊ／ｍ２）提高了一倍。     

Covalent grafting of triazine derivatives onto graphene oxide for preparation of epoxy composites with improved interfacial and mechanical properties

Interface interactions are the important problems in improving the mechanical properties of graphene and polymer composites. In this work, a simple method is proposed to prepare epoxy composites with admirable properties through constructing dendrimers with cyanuric chloride (TCT) and diethylenetriamine (DETA) onto graphene oxide (GO) surface. The FTIR, XRD, XPS, Raman spectroscopy, SEM and TEM were used to confirm the successful grafting of TCT and DETA molecules onto the surface of GO. The interfacial adhesion between GO–TCT–DETA and epoxy resin is enhanced due to the formation of a strong chemical bond between the amino group on the GO surface and the epoxy resins. The tensile and flexural strength of GO–TCT–DETA/epoxy composites have considerable improvement (40.79 and 48.56%) compared with that of epoxy resin due to stronger interfacial interaction. In addition, the strengthening mechanism and dispersion of GO–TCT–DETA in epoxy matrix were also demonstrated.     

Surface modification of nano-SiO2 by in situ grafted polymerization of butyl methacrylate

Silane coupling agent was used to introduce polymeric groups that was C=C onto the surface of nano-SiO₂ particles by self-assembling technique. Then, in situ grafted polymerization was carried out between the functionalized particles and butyl methacrylate monomers under the action of an initiating agent to accomplish the surface modification of nano-SiO₂. The effect of different reaction conditions on grafting percentage was studied, and analyses of FTIR, TEM, and TG-DTA results show that new organic chains were introduced onto the surface of nano-SiO₂, and the dispersion stability of nano-SiO₂ in THF was obviously improved. The text was submitted by the authors in English.     

链长对炭纤维/聚芳基乙炔复合材料界面性能的影响

采用在炭纤维表面接枝含有不同链长的偶联剂的方法, 研究了链长对炭纤维/聚芳基乙炔复合材料界面性能的影响。纤维和树脂的浸润性通过纤维表面能的测定以及纤维表面能和浸润性的讨论进行了评价。通过复合材料界面剪切强度测试以及断口形貌分析对炭纤维/聚芳基乙炔复合材料的界面性能进行了研究。结果表明, 随着炭纤维表面链长的增长, 炭纤维/聚芳基乙炔复合材料的界面粘结性能随之提高。界面粘结性能的提高主要归因于接枝于炭纤维表面的偶联剂的分子链和聚芳基乙炔树脂分子链发生了物理缠结作用, 并且这种缠结作用随着纤维表面分子链的长度的增加而增强。      

PB-g-SAN接枝共聚物的接枝率对ABS树脂结构与性能的影响

采用种子乳液聚合技术在聚丁二烯(PB)乳胶粒子上接枝共聚单体苯乙烯(St)和丙烯腈(AN),通过改变PB的含量合成了一系列具有不同接枝率的PB-g-SAN接枝共聚物(即ABS接枝共聚物),将其与SAN树脂进行熔融共混制得ABS树脂,考察了ABS接枝共聚物的接枝率对ABS树脂结构和性能的影响。结果表明,SAN共聚物在PB橡胶粒子上的接枝可分为‘内接枝’和‘外接枝’,外接枝程度影响PB橡胶粒子在SAN基体中的分散,而内接枝程度显著地影响PB橡胶粒子的内部形态结构。通过抑制内接枝,可提高ABS树脂的冲击韧性和拉伸强度;提高外接枝程度可改善ABS树脂的断裂伸长率。     

Tetra-anionic porphyrin loading onto ZnO nanoneedles: A hybrid covalent/non covalent approach

A stepwise surface functionalization procedure, based on hybrid covalent and non-covalent approach is herein proposed to anchor tetra-anionic meso-tetrakis(4-sulfonatophenyl)porphyrin on ZnO nanorods. Carboxyalkylphosphonic acids have been proven effective to form stable self-assembled monolayers through the surface grafting of –PO₃H₂ headgroups. The exposed carboxylic functionalities are suitable for the successful grafting of cationic poly-l-lysine that drives, in water, the non-covalent anchoring of the anionic porphyrin. A stepwise surface characterization, provided by X-ray photoelectron spectroscopy, elucidates the multilayers deposition and surface composition after each process step, thus, giving interesting insights on the chemical speciation of the exposed functionalities. UV–vis spectroscopy confirms the role of ZnO morphology to increase the porphyrin loading onto the investigated surfaces. The proposed approach is effective to achieve deposition of anionic porphyrins on ZnO nanostructures and combines the robustness of covalent functionalization with the versatility and full reversibility of the non-covalent strategies.     

Immobilization of a heteropolyacid catalyst on the aminopropyl-functionalized mesostructured cellular foam (MCF) silica

Mesostructured cellular foam (MCF) silica with high surface area (>600 m²/g) and large pore volume (≈1.16 cm³/g) was synthesized via a surfactant templating method. The MCF silica was then modified by grafting 3-aminopropyl-triethoxysilane (APTES) to create a positive charge on the surface, and thus, to provide sites for the immobilization of H₃PMo₁₂O₄₀. By taking advantage of the overall negative charge of [PMo₁₂O₄₀]³⁻, the H₃PMo₁₂O₄₀ catalyst was chemically immobilized on the aminopropyl group of the surface modified MCF silica as a charge matching component. The mesopore structure of MCF silica was maintained even after the surface modification step and the subsequent immobilization step of H₃PMo₁₂O₄₀. The H₃PMo₁₂O₄₀ species were finely and molecularly dispersed on the surface modified MCF silica via chemical immobilization.     

Impact of Zr/Ti ratio in the PZT on the photoreduction of silver nanoparticles

Silver nanoparticle deposition from an aqueous solution of silver nitrate onto the surface of PZT thin films of stoichiometric compositions PbZr_0.3Ti_0.7O₃ and PbZr_0.52Ti_0.48O₃ has been investigated. The impact of Zr/Ti ratio on the photochemical properties of PZT is shown by the preferential growth of silver nanoparticles onto the surface. Photoreduction of silver occurs on both c⁺ and c⁻ domains on PbZr_0.52Ti_0.48O₃ whereas it occurs only on c⁺ domains on a PbZr_0.3Ti_0.7O₃ surface. The difference in deposition pattern is attributed to difference in magnitude of spontaneous polarization, effective hole concentration and band gap of the two samples which impacts shape and width of space charge layer in the two samples resulting in a change in band bending at the surface.     

环氧丙烯酸阴极电泳涂料的研制及涂装工艺对涂膜性能的影响

通过接枝共聚的方法在环氧树脂主链上接枝丙烯酸酯类单体,再配以其他物质合成出自交联的阴极电泳涂料用的丙烯酸接枝环氧树脂,以此为主体树脂制备出白色的电泳涂料.探讨了阴极电泳涂料的电泳工艺参数对涂膜性能的影响.结果表明:在电泳电压为90 V左右,漆液固体分为16%,pH值为5.8,电泳时间为2.0～3.0min条件下.可获得...     

Effects of surface-functionalized multi-walled carbon nanotubes on the properties of poly(dimethyl siloxane) nanocomposites

The effects of surface-functionalized multi-walled carbon nanotubes (MWNTs) on the properties of poly(dimethyl siloxane) (PDMS) nanocomposites are investigated in the present study. The surface functionalization of MWNTs is carried out by diphenyl-carbinol functionalization followed by reaction with multifunctional silane, 3-aminopropyltriethoxisilane. Fourier transform infrared spectroscopy (FT-IR) and energy dispersion spectroscopy (EDS) analysis are used to confirm the presence of diphenyl-carbinol and silane on the surface of the MWNTs. The effects of the MWNTs’ surface treatment on the thermal and electrical properties of poly(dimethyl siloxane)-based (PDMS) nanocomposites are also studied. The results show that the grafting of silane molecules onto diphenyl-carbinol-functionalized MWNTs (SD-MWNTs) improves the dispersion of MWNTs in PDMS; this subsequently enhances the thermal conductivity and dynamic mechanical properties as compared to those containing unmodified (U-MWNTs) and diphenyl-carbinol-functionalized MWNTs (D-MWNTs). The electrical conductivity of the nanocomposites is shown to decrease due to the wrapping of MWNTs with non-electrical-conducting organic materials.